1. Field of the Invention
The present invention relates to a method of controlling combustion in a furnace of the type including a mixing/stirring region where unburnt gas and secondary combustion air are mixed and stirred together so that combustible material, e.g., urban refuse, industrial waste or the like is effectively burnt.
2. Description of the Prior Art
Generally, urban refuse, various kind of industrial waste and so forth are substantially different from each other in configuration or size. This makes it difficult to practically design and construct a combustible waste material feeding machine on a commercial basis under the condition that a quantity of waste material to be fed into a furnace per unit time is correctly maintained. In addition, urban refuse, industrial waste and so forth differ in quality, and any variation in quality and/or quantity of combustible waste material to be fed into the furnace is directly converted into a variation in quantity and/or quantity of the resulting exhaust gas. Therefore, when the furnace is provided with a fixed supply of combustion air, there arises a problem that an excess or shortage of oxygen occurs. If the furnace is operated with an insufficient quantity of oxygen, unburnt gas is discharged from the furnace. On the contrary, when the furnace is operated with an excessive quantity oxygen, i.e., an excessive quantity of combustion air, the resultant combustion gas is cooled to an undesirable extent. This means that incomplete combustion takes place with the result that unburnt gas is discharged from the furnace. In view of the aforementioned problems, to make sure that an excessive or insufficient supply of oxygen does not occur in the furnace, a density of oxygen in the resultant combustion gas is normally measured to correctly control the quantity of combustion air to be fed into the furnace.
A proposal has been heretofore made such that shape and size of a combustion chamber of the furnace be designed in a different manner so as to allow combustion air to effectively come into contact with unburnt gas and moreover the blowing speed of the combustion air is varied so that the combustion air is effectively mixed with the unburnt gas.
However, with the aforementioned conventional method of controlling combustion in a furnace, when the furnace is controlled while varying a quantity of combustion air to be fed into the furnace, the blowing speed of the combustion air varies. Thus, when the furnace is operated under conditions different from designed points, there arises another problem that the configuration of the furnace does not correctly match the blowing speed of the combustion air.